Laboratory experiment 4.
Deformation and strain measurement with DSP-equipment, Speckle.
A tensile test on a Macrolon, or polycarbonate, sheet specimen will illustrate the ability to
measure in-plane deformations and strains. In particular the effect of a hole on strains and
stresses will be investigated.
1. Determine isotropic linear elastic material properties of the polycarbonate
1a. Verify the linearity in the stress-strain relation. For this you need the load signal
2. Detect the strains over the specimen surface and in particular around the hole
3. Compare the strain results with FE solution of strains and stresses
4. Compare the maximum measured and maximum FE stresses with handbook solution for stress
concentration
The department has only one DSP-Speckle equipment. Therefore the laboratory time for each
group is shorter than normal. Also, the part of the strain evaluation in which the measurement
system is required has to be finalized during the laboratory. The specimen, which has been
painted with a random speckle pattern prior to the exercise, will be rigged in the test machine.
The DSP-system is connected and adjusted to suitable light conditions.
You will use a servo-hydraulic test machine, the test machine computer and the DSP-Speckle
equipment with ARAMIS computer system. There is no control connection between the different
equipment. Therefore you will arrange everything, start data capturing and experiment manually.
The laboratory supervisor will show you the basic ARAMIS commands for visual displacement
measurements and data processing.
The laboratory preparation will include the following steps:
1 Setup the ARAMIS system and file
2 Prepare picture capturing in ARAMIS
3 Prepare Instron test machine system for loading the specimen with a linear double ramp with
maximum load 4 kN and load rate 0,4 kN/sec. Remember load limits: min = -0.1 kN and
max = 4.2 kN.
4 Prepare test machine computer to show load-deformation cycle with the program dragjq1.
5 Make sure load signal is included into ARAMIS capturing
Test
1 Start capturing pictures in ARAMIS
2 Start capturing the load-displacement view on the machine computer
3 START test on Instron control panel
4 FINISH on Instron control panel when test cycle is done (POSITION & LOAD PROTECT)
5 Stop capturing with ARAMIS
6 Stop computer load-displacement measurement
Post processing on ARAMIS
1 Create surface images of strains x, y and xy.
2 Plot curves showing strain at selected points against load (longitudinal far-field stress)
3 Save your pictures and your load-strain data.
4 Remember to measure the specimen cross-section.
Move files to your USB
Laboratory report
Your laboratory report shall include:
• A description of the tension test
• An evaluation of isotropic linear elastic material properties (E, ν). Compare with tabulated
values
• Images of strain components (εx , εy , γxy )
• FE simulation of the corresponding strains using the measured elastic material properties –
present result and comment on agreement
• FE calculated stress images (σx , σy , τxy ). State the nominal and maximum stresses.
• Handbook calculation of stress concentration – comment on agreement with measured and FE
result.